Ask Tom: Is the 'Arizona monsoon' really a monsoon?

The term monsoon refers to a seasonal change in wind direction driven by huge temperature differences that develop between land masses and a nearby ocean. In winter, the air over land is relatively cool and oceanic air is warm; air flows from land to water. In summer, it's the opposite; air flows from water to land.

It's natural to think of southern Asia when monsoons are mentioned, but the Arizona (and southwestern U.S.) monsoon is real. It extends from about mid-July through mid-September. While producing only a fraction of south Asia's monsoon rain totals, Arizona monsoon totals aren't always light. In 1964, Tucson recorded 13.49 inches above its two-month monsoon season average of 5.46 inches.